转换“地图"；反对"SpatialPolygon"目的 [英] Converting a "map" object to a "SpatialPolygon" object

问题描述

我猜有一个简单的解决方案可以解决我遇到的问题，但是我遇到了麻烦.

I am guessing there is a simple solution to the problem I have been having, but I am having some trouble.

我正在尝试转换以下map对象:

I am trying to convert the following map object:

require(maps)
usa <- map("state")

使用map2SpatialPolygons函数将

转换为SpatialPolygon对象:

require(maptools)
usa.sp <- map2SpatialPolygons(usa, IDs=usa$names,proj4string=CRS("+proj=longlat"))

我一直收到以下错误:

Error in map2SpatialPolygons(usa, IDs = usa$names, proj4string = CRS("+proj=longlat")) : 
  map and IDs differ in length

经过研究，在应用函数.NAmat2xyList(cbind(map$x, map$y))之后，ID似乎长63，map对象长169(我找不到源).

After some research, it looks like the IDs have length 63 and the map object has length 169 after applying the function .NAmat2xyList(cbind(map$x, map$y)) (for which I cannot find the source to).

有人有什么想法吗?这是usa地图对象的结构:

Anyone have any ideas? Here is the structure of the usa map object:

> str(usa)
List of 4
 $ x    : num [1:1705] -88.4 -88.1 -88 -87.9 -87.8 ...
 $ y    : num [1:1705] 30.4 30.4 30.8 30.6 30.3 ...
 $ range: num [1:4] -124.7 -67 25.1 49.4
 $ names: chr [1:63] "alabama" "arizona" "arkansas" "california" ...
 - attr(*, "class")= chr "map"

推荐答案

仅在文本使用R进行应用空间数据分析"中找到了一些代码.效果很好！

Just found some code in the text "Applied Spatial Data Analysis with R". It works great!

require(maps)
usa <- map("state", fill = TRUE)

require(sp)
require(maptools)
IDs <- sapply(strsplit(usa$names, ":"), function(x) x[1])
usa <- map2SpatialPolygons(usa, IDs=IDs, proj4string=CRS("+proj=longlat +datum=WGS84"))

这篇关于转换“地图"；反对"SpatialPolygon"目的的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！